Go Agent writes out dhclient config on Ubuntu

 * Introduces Platform to agent
 * Infrastructure delegates to platform through interface
 * Platform is specified by -P

Signed-off-by: Jeffrey Peckham <peckham@pivotallabs.com>
Explicitly including directories in gemspecs

Signed-off-by: Jeffrey Peckham <peckham@pivotallabs.com>
Restart dhcp client after writing config file

Signed-off-by: Jeffrey Peckham <peckham@pivotallabs.com>
Invoking root profile during stemcell build stages.

- Needed to find go in PATH

Signed-off-by: Jeffrey Peckham <peckham@pivotallabs.com>